The prior art practice in Claus reaction processing has attempted various techniques for recovery of both sulfur and water from a Claus reaction effluent. Typically, sulfur has been recovered independently or in a different stage of processing from water of reaction if the latter is recovered at all. Under operation of high pressures, it is possible, as is known in the prior art, to condense water without solidifying sulfur so as to avoid a sulfur plugging problem. In all of the solid sulfur recovery processes, it is recognized that sulfur plugging of process apparatus is a potential problem. It is recognized by the sulfur processing industry that removal of water of reaction at an intermediate stage in Claus processing will affect improvements in the overall Claus reaction to achieve more complete conversion of hydrogen sulfide to elemental sulfur.
U.S. Pat. No. 2,413,714 is directed to a Claus process, including a combustion furnace 3, wherein a Claus reaction effluent passes through a catalytic reactor 8 and water and liquid sulfur are condensed in a tower 9, subjected to a spray of water through line 16. At column 5, lines 43-45, it is stated that the spray of water is in the form of a "finely divided form and as film on the walls of condenser 9 and reservoir 10". The process is operated at a pressure of at least 20 psi gauge. Final water/ sulfur separation is affected in a countercurrent contact tower 11. The patented process attempts to recover solid sulfur simultaneous with the recovery of water of reaction from a Claus gas at a temperature at least above the freezing point of sulfur.
U.S. Pat. No. 3,681,024 discloses a Claus reaction process wherein acid gas, oxygen and recycle gas are combusted in a furnace 2 and further in a catalytic reactor 18 before the Claus reaction effluent is introduced into a countercurrent water tower 26. The effluent is scrubbed to remove sulfur, which forms solid sulfur in the top of the tower 26 proximate to the dispenser 30 and forms a slurry or liquid sulfur at the bottom of the tower 26, proximate to the dispenser 32, depending upon the temperature. The pressure of the system is recited to be in the range of 0 to 50 psig. No teaching is made with regard to the avoidance of sulfur plugging in any area of the tower 26 which is susceptible to solid sulfur formation. In the preferred embodiment, the patented process would not have a sulfur plugging problem at the base of the tower 26 because of the preferred form of the sulfur being in its molten form.
U.S. Pat. No. 3,822,341 is directed to a Claus process in which acid gas is combusted with an oxygen containing gas in waste heat boiler 8 and further reacted in a catalytic reactor 24 before being combined with tail gas and introduced in a separation vessel 44 containing liquid water. Solid sulfur is purportedly deposited on the froth 56 and removed as powdered sulfur in line 60. Water is removed in line 64 and stripped of sulfur dioxide with an oxygen containing gas purge. The desulfurized Claus effluent in line 40 is further reacted in catalytic reactors. Sulfur solidification in dispersion nozzle 52 is not addressed by the patent.
U.S. Pat. No. 4,158,039 discloses an apparatus for separating sulfur from an aqueous sulfur suspension which is heated above the melting point of sulfur through heating coils 20. The sulfur is separated by the action of heat and agitation by a mixing device. Molten sulfur is removed in line 34. This sulfur separation patent does not address the removal of solid sulfur from a Claus gas.
Additional patents in the prior art directed to the field of Claus processing and sulfur recovery of more general interest include U.S. Pat. Nos. 2,258,305, 3,798,316, 4,138,473, 4,302,434, 4,426,369, 4,464,309, 4,481,181, 4,526,590 and 4,601,330. Additionally, the Abstract of German Patent No. DE3607029A discloses separation of sulfur from its dispersion in water and European patent application No. 0 234 894 discloses a Claus process including a water condensation step downstream of the first sulfur condenser.
European patent application No. 0 082 579 teaches a self-regulating process for removal of hydrogen sulfide from gases comprising the absorption of a first part of the hydrogen sulfide from the gas stream in an aqueous solution of sulfur dioxide to form elemental sulfur, separation of the remaining amount of hydrogen sulfide from the gas stream by a conventional absorption system (9), recovery of the hydrogen sulfide from the conventional absorption system, conversion of the recovered hydrogen sulfide to sulfur dioxide and use of the sulfur dioxide to form the aqueous solution of sulfur dioxide used to absorb the first part of the hydrogen sulfide.
U.S. Pat. No. 3,911,093 has a process for recovering sulfur values from gas emissions by absorbing SO.sub.2 in an aqueous solution comprising a mixture of Na.sub.2 HPO.sub.4 and NaH.sub.2 PO.sub.4 at a pH between about 2.5 and about 5 at an absorption temperature between about 85.degree. and about 200.degree. F., treating the phosphate solution containing absorbed SO.sub.2 with H.sub.2 S to produce sulfur, separating the sulfur from the phosphate solution and recycling the phosphate solution to the absorber. Provision is made to remove sulfate, which builds up in phosphate absorbent, by crystallizing sulfate from a purge stream. The process is particularly useful in the field of pollution abatement for recovering SO.sub.2 from the off-gas obtained from a Claus-type reactor system.
None of the prior art addresses an efficient technique for simultaneous removal of water of reaction and solid sulfur from a Claus gas without sulfur deposition or plugging of process apparatus and the efficient separation of sulfur from water, as is fully achieved by the process and apparatus of the present invention detailed below.